For the continuum gas opacity,
we use very-high-resolution LTE absorption coefficients with a constant step size in wavenumber of 0.01 cm\(^{-1}\) , corresponding to
a spectral resolution \(R=1.5\times 10^6\) . This is sufficient to resolve line cores over the relevant \((P,T)\)  domain [1]}, [2]}. We assume a solar-metallicity [3]} mixture. The opacities of the individual species were calculated with HELIOS-K [4]}, [5]}. All atoms and ions up to a proton number \(Z=40\)  are included,
and so are the continua of H\(^-\)  and collision-induced absorption (CIA) of
H\(_2\) –H\(_2\) , He–H, and H\(_2\) —He.
Molecular absorption is included for H\(_2\) O , CO, TiO, SH, and VO.
Abundances were determined by chemical equilibrium calculations for the gas phase as provided by FastChem [6]}.
Where needed, we extrapolate the fit of the equilibrium constants beyond their tabulated range of \(T=100\) –6000 K to calculate opacities from \(T=100\)  to \(10^4\)  K.
A detailed description of chemical and opacity data for the atoms and ions can be found in [7]}.
Molecular absorption coefficients are based on the Exomol line lists where available [8]}, [9]}, [10]}, [11]} and on HITEMP [12]} otherwise.
The CIA data are taken from the HITRAN database [13]}.
